Condensed Consolidated Statement of Changes in Stockholders' Equity and Noncontrolling Interests (USD $) In Thousands, except Share data, unless otherwise specified	Total	Redeemable Noncontrolling Interests	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests	Series C Preferred Stock	Series D Convertible Preferred Stock	Series E Preferred Stock
Balance at Dec. 31, 2011	$ 3,416,859	$ 16,034	$ 616	$ 3,028,558		$ (34,511)	$ 42,558	$ 129,638	$ 250,000
Balance (in shares) at Dec. 31, 2011			61,560,472
Increase (Decrease) in Stockholders' Equity
Net income	58,416	411			56,854		1,151
Unrealized loss on marketable securities	(119)					(119)
Unrealized gain on interest rate swap agreements	4,506					4,506
Foreign currency translation (loss) gain	(7,233)	2				(7,246)	11
Contributions by noncontrolling interests	1,125						1,125
Distributions to noncontrolling interests	(598)	(630)					(598)
Issuance of common stock, net of offering costs	39,861		5	39,856
Issuance of common stock, net of offering costs (in shares)			538,086
Issuance of Series E Preferred Stock, net of offering costs	124,868			(5,132)						130,000
Issuances pursuant to stock plan	10,197		1	10,196
Issuances pursuant to stock plan (in shares)			151,415
Redemption of Series C Preferred Stock	(129,638)			5,978	(5,978)			(129,638)
Dividends declared on common stock	(62,348)				(62,348)
Dividends declared on preferred stock	(14,715)				(14,715)
Distributions in excess of earnings				(26,187)	26,187
Balance at Jun. 30, 2012	3,440,768	15,817	622	3,053,269		(37,370)	44,247			130,000
Balance (in shares) at Jun. 30, 2012			62,249,973
Balance at May. 31, 2012
Increase (Decrease) in Stockholders' Equity
Dividends declared on common stock	(32,000)
Dividends declared on preferred stock									(4,400)	(2,800)
Balance at Jun. 30, 2012	$ 3,440,768								$ 250,000	$ 130,000